1. Field of the Invention
The invention relates to variable geometry turbochargers for internal combustion engines and, more specifically, to control schemes for such variable geometry turbines.
2. Description of the Related Art
The turbocharger was first proposed by Dr. Alfred Buchi at the beginning of the Twentieth Century. The turbocharger or turbo supercharger, as otherwise known, was an advanced concept to increase the efficiency of internal combustion engine and, more specifically, compression ignition engines. The turbocharger included a turbine, driven into rotation by the otherwise wasted products of combustion from the engine, and connected to a compressor for pressurizing the inlet air to the engine for combustion to a pressure level higher than the ambient pressure. Such a system allowed greater density of the charge mixture and, therefore, greater given output for an engine so equipped. Over the years, the deficiency of the turbocharger in responding to transient operator demand increases was addressed by variable geometry turbines (VTG). In such an arrangement, the turbine inlet area is variably reduced either by a movable ring or variable inlet guide vanes to provide a lower flow area into the turbine and, therefore, a higher gas flow velocity which, in turn, acted on the turbine to increase the power to the compressor and, thus, the response to the step increase in operator demand.
The request for increased power is complicated by the overlay of emissions regulations on the primary operational parameters of a compression ignition engine of power and efficiency. The emissions requirements generally mean that acceleration of an engine is smoke limited, that is, the fueling cannot exceed an amount relative to the available air flow that generates smoke in the form of particulates. Such a requirement alters the mechanism and control scheme for controlling the variable geometry turbine in such a way that smoke is avoided. However, such control schemes leave very much to be desired in terms of responsiveness of the variable geometry turbine in smoke limiting situations.
Accordingly, what is needed in the art is a control system for a variable geometry turbine that maximizes responsiveness to transient increases in demand, or turbine power output.